Design Guidelines for High Performance Industrial Furnaces - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 251

Outlet
Inlet
Z
Y
X
FIGURE 5.6 Analysis model.
furnace temperature distribution deviation; it is especially noticeable when the wall
is longer than 80%. A longer partition wall also results in a larger heat flux in the
material to be heated, and the heat flux to the direction of burner axis changes from
concave distribution curves (curves less than 60%) to convex curves, and for curves
over 80%, the deviation increases. It also means that the longer the partition wall
is, the smaller the convection heat flux, and for curves over 80%, it becomes smaller
by around 15%. To summarize, the optimum length of the partition wall is 70% ±
10% of the effective furnace length (in the direction of the longer side of the heating
material), and in this range the furnace temperatures are higher and their deviation
is smaller.
5.1.3.4 Lower Part of Furnace
A number of tests using the model test furnace shown in Figure 5.15 yielded several
significant results. In one experiment where the heating pattern of the furnace
remained constant, the comparison of the furnace temperature distribution was made
between combustion with air at normal temperature and combustion with air at a
high temperature. The result showed that the distribution was more uniform during
combustion with high temperature air than combustion with normal temperature air
as shown in Figures 5.16 and 5.17 . Where heat input was constant at 930 kW, the
time required for the surface temperature of steel at the burner side to rise from
normal temperature to 1100˚C was compared with conditions where normal tem-
perature air was used. The result showed that temperature rise from combustion with
high temperature air was quicker, as shown in Figure 5.18 .
In the comparison with 1200˚C of the furnace temperature with 1.2 MW of
combustion, it was found that in the case of combustion with high temperature air,
the temperature of steel near the skids was higher and the difference of temperatures
between the portion of the steel directly above the skids and the portion around the
middle of the steel was smaller than with normal combustion ( Figure 5.19 ) . By